FR3089429A1 - Method and apparatus for purifying a hydrogen-rich gas - Google Patents

Abstract

In a process for separating a mixture (1) rich in hydrogen also containing argon and / or carbon monoxide and / or methane and / or at least one hydrocarbon heavier than methane, the mixture is separated in a phase separator (9) to form a gas flow (11) rich in hydrogen but depleted in argon and / or methane and / or carbon monoxide and / or at least one hydrocarbon heavier than methane and it is heated at least a first part (2) of the gas flow in the heat exchanger to serve as the first product rich in hydrogen, a second part (13 of the flow is sent to a washing column (17) whose head gas constitutes a second product (3, 8) Figure of the abstract: Fig. 1

Description

Description

Title of the invention: Method and apparatus for purifying a hydrogen-rich gas

The present invention relates to a method and an apparatus for purifying a hydrogen-rich gas, for example containing at least 60 mol% of hydrogen, preferably at least 80 mol% of hydrogen, or even at minus 90% mol of hydrogen.

A hydrogen-rich gas can contain compounds such as CO, methane, argon and possibly at least one hydrocarbon heavier than methane; it can be purified using a nitrogen washing process in a cold box. After treatment, the hydrogen contains lower amounts of CO, methane, argon, etc., on the other hand, it is enriched in nitrogen.

The nitrogen washing processes usually produce only one type of hydrogen.

The nitrogen washing processes are relevant when it is possible to add nitrogen to the treated hydrogen. This is for example the case for ammonia synthesis plants. For this type of plant, the synthesis gas is a mixture of H ₂ and N ₂ . Thus, the nitrogen washing process makes it possible both to purify the hydrogen and to add nitrogen to have an adequate N ₂ / H ₂ mixture (H ₂ / N ₂ ratio of 3 / 1).

The nitrogen washing process is not suitable if the purified gas must not contain nitrogen.

If you want to produce two types of hydrogen, hydrogen containing nitrogen, and hydrogen containing no nitrogen, the hydrogen is separated upstream of the cold box. Hydrogen which is not sent to the cold box is not enriched in nitrogen by the nitrogen washing process, on the other hand, it is not purified into CO, methane or argon.

The present invention makes it possible to produce two types of hydrogen: purified hydrogen containing nitrogen (for example, for an ammonia synthesis plant), and purified hydrogen not containing (or little) nitrogen (for example, for a methanol synthesis plant).

The invention provides as an improvement over the state of the art, the reduction of impurities in H ₂ not enriched in nitrogen. This H ₂ can be used, for example, to synthesize methanol. The reduction of impurities, in particular of inert compounds, makes it possible to increase the efficiency of the synthesis of ammonia.

The nitrogen washing process has been used since the 1960s, as for example in the process of US3312075 or that of US4765814. As mentioned previously, it can be used to treat H ₂ -based gases which then go

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Supply ammonia synthesis plants.

The proposed invention is a nitrogen washing process, which makes it possible to produce two types of hydrogen:

• hydrogen “conventionally” produced by nitrogen washing processes, ie hydrogen depleted in typical impurities such as carbon monoxide and / or methane and / or argon, but which, by against, is enriched in nitrogen. This hydrogen is produced by following the various stages described above in the “state of the art” section.

• hydrogen impoverished in impurities, including nitrogen. This hydrogen is produced by cooling the gas to a cryogenic temperature. Part of the gas condenses, the impurities are concentrated in the liquid phase, the gas phase is enriched in H ₂ .

The proposed process consists in cooling the feed flow to a temperature of around -182 ° C, via cryogenic heat exchangers. Part of the gas condenses. The condensate is then separated from the gas phase in a phase separator. The gas phase leaving the phase separator is enriched in hydrogen and depleted in impurities such as carbon monoxide and / or methane and / or argon etc. This gas phase is then separated into two parts: part of the hydrogen is sent to the washing column with nitrogen, the other part is reheated in the cryogenic heat exchangers. This second part constitutes the H ₂ not enriched in nitrogen.

The hydrogen sent to the nitrogen washing column is recovered, in purified form, at the top of the column. In this basic case, the hydrogen is heated in the exchanger before topping up with liquid nitrogen.

When nitrogen and hydrogen are mixed, the gas cools. The mixture is therefore reintroduced at a colder point on the exchanger.

Note that, depending on the case, the H ₂ can be reheated to an intermediate temperature (between -182 and 30 ° C), before carrying out the nitrogen addition.

The liquid recovered in the tank of the washing column (liquid rich in nitrogen) is expanded.

The refrigeration balance of the unit is ensured by adding liquid nitrogen. The LN2 is expanded, then mixed with the liquid recovered in the tank of the washing column. The mixture is then reheated in the cryogenic exchangers.

The condensate recovered after cooling the feed flow (methane-rich condensate) is also expanded and sent to cryogenic exchangers.

According to an object of the invention, there is provided a method for separating a mixture rich in hydrogen also containing argon and / or carbon monoxide and / or methane and / or at least one hydrocarbon heavier than methane and possibly nitrogen in which:

at. the mixture is cooled in a heat exchanger,

b. at least part of the mixture is condensed to form a two-phase flow, the gas is separated in a phase separator to form a gas flow rich in hydrogen but depleted in argon and / or methane and / or carbon monoxide and / or at least a hydrocarbon heavier than methane and a first part of the gas flow is heated in the heat exchanger to serve as the first product rich in hydrogen,

vs. a second part, or even the rest, of the gas flow or the rest of the mixture is sent to a washing column,

d. we send a flow of liquid nitrogen at the top of the washing column,

e. a gas rich in hydrogen, depleted in argon and / or methane and / or carbon monoxide and / or at least one hydrocarbon heavier than methane and containing nitrogen than nitrogen is removed from the head of the washing column it is heated in the heat exchanger, to serve as a second product, possibly after having been mixed with liquid and / or gaseous nitrogen, and

f. a liquid flow is taken out of the tank of the washing column.

According to other optional aspects:

• the first product contains less than 5% mol of nitrogen, or even less than 1% mol of nitrogen.

• the second product contains less methane and / or argon and / or carbon monoxide and / or at least one heavier hydrocarbon than methane than the first product.

• the first product contains less nitrogen than the second product.

• the hydrogen-rich gas leaves the head of the washing column containing more than 1 mol%. nitrogen, preferably more than 5% mol. nitrogen. ...

• the liquid from the phase separator is expanded, it is separated in an additional phase separator, the gas and the liquid from the additional phase separator are heated in the heat exchanger.

• the frigories are supplied at least mainly, preferably entirely by sending liquid nitrogen from an external source to a phase separator of the process.

According to another object of the invention, there is provided an industrial process comprising a methanol synthesis process supplied by the first product of the process as described above and an ammonia synthesis process supplied by the second product of the process as described above.

According to another object of the invention, there is provided an apparatus for separating a mixture rich in hydrogen also containing argon and / or carbon monoxide and / or methane and / or at least one hydrocarbon heavier than methane and possibly nitrogen comprising a heat exchanger, a phase separator, a washing column, means for sending the mixture to cool and partially condense in the heat exchanger, means for send at least part of the partially condensed mixture to the phase separator, means for sending part of the gas from the phase separator to heat up in the exchanger as first product, means for sending a second part, or even the rest, of phase separator or part of the mixture to the washing column, means for sending a flow of liquid nitrogen at the head of the washing column, means for leaving a gas rich in hydrogen from the head of the washing column, app provided with argon and / or methane and / or carbon monoxide and / or at least one hydrocarbon heavier than methane and containing nitrogen and means for sending the hydrogen-rich gas to heat up in the heat exchanger, to serve as a second product, possibly after having mixed it with liquid nitrogen and means for removing a liquid flow from the tank of the washing column. According to a variant of the invention, there is provided a unit comprising an apparatus as described above, a methanol synthesis unit, an ammonia synthesis unit, means for sending the first product to the methanol synthesis unit and means for sending the second product to the ammonia synthesis unit.

The invention will be described in more detail with reference to [fig.l], [Fig.2], [Fig.3] and [Fig.4] which represent methods according to the invention.

[Fig.l] shows a process for producing two products 2, 3. A gas flow 1 rich in hydrogen, containing at least 60% mol of hydrogen, preferably at least 80% mol of hydrogen, or even at at least 90 mol% of hydrogen also contains argon and / or carbon monoxide and / or methane and / or at least one hydrocarbon heavier than methane and optionally nitrogen. An example of composition is given in the material balance which follows.

The flow 1 is cooled from 40 ° C to -70 ° C in a heat exchanger 23 and then from -70 ° C to -182 ° C in a heat exchanger 25. At a pressure of 52 bars and partially condensed, it is sent to a phase separator 9. The gas 11 from this separator 9 is divided into two. A first part 2 serves as the first product rich in hydrogen, being enriched in hydrogen and depleted in argon and / or carbon monoxide and / or methane and / or at least one hydrocarbon heavier than methane and optionally nitrogen compared at flow 1.

A second part 13 which is the rest of the flow 11 is sent to the tank of the washing column 17 where it is washed with a flow of liquid nitrogen 21 injected at the top of the column. This nitrogen 21 is produced by condensing nitrogen gas 4 from an external source in the exchangers 23, 25.

This results in a gas flow 8 slightly depleted in hydrogen compared to flow 1 but also depleted in argon and / or carbon monoxide and / or methane and / or at least one hydrocarbon heavier than methane. On the other hand, it is enriched in nitrogen, due to washing, with a content of almost 10% mol for the example.

This second hydrogen-rich product 8 can be mixed with gaseous or liquid nitrogen 19, for example to form a mixture of nitrogen and hydrogen 3 adapted to be converted into ammonia.

The tank liquid 10 of the column 17 is expanded in a valve VI and mixed with a flow of liquid nitrogen 7 from a storage and regulated by a valve V2. The mixture is sent to a phase separator 27. The gas 29 and the liquid 31 of the separator 27 are mixed and heated in the exchangers 23, 25. The mixture formed 5 is rich in nitrogen (almost 50% mol) and can serve as fuel.

The tank liquid 15 of the separator 9 is expanded in a valve V3 and sent to a phase separator 33. The liquid 35 of the separator 33 vaporizes in the exchanger 25 and is mixed with the heated gas 37 of the separator 33 to form a flow 6 rich in methane which is used as fuel.

Liquid nitrogen 19 is added to the flow 8 after being cooled in the exchanger 23 and a little in the exchanger 25. The mixture of liquid nitrogen and gas is returned to the exchanger 25 at a lower temperature than the liquid or gas before mixing.

Preferably, the second product 8 contains less methane and / or argon and / or carbon monoxide and / or at least one heavier hydrocarbon than methane than the first product 2.

Preferably the first product 2 contains less nitrogen than the second product 8.

Thus the method allows to produce a first product 2 containing very little nitrogen (in the example less than 1% mol) but rich in hydrogen and a second product 8 rich in hydrogen but also containing nitrogen.

The cold behavior of the process is ensured by the arrival of liquid nitrogen 7 from an external source. No flow is relaxed in a turbine.

An apparatus operating according to this process can be incorporated into a unit comprising a methanol synthesis unit and an ammonia synthesis unit, means being connected to send the first product to the methanol synthesis unit and means being connected to send the second product to the ammonia synthesis unit.

Material Balance

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[Tables 1]

......... ï .......... ï ....... 4 ....... ....... 7 '! ......... 3 ........ [ ....... 8 ........ ï ........ 2 ....... ] .......... g ....... f ........ 5 ........] Units | AtnWReifofl $ fi? § LHï : {after ΐ; & opatîtt Njj i (swtfc ôdionne) $ Prsmter § product H? i Grin gas © si; § CHs Gazrîeha § w »#? § P I bar g) 51. &) 53.3 <c: e : 49.7 i 7 ; ) I- ⁸ i 4.0) T ! 40 ^; d 7 ' * 190 ] 42 ) 43 ii 42) “Q 1 3—7SÎ Γ Her P '»2 T Î8Î 353 f Tao / B ' 4 sswS ' ï 7,383 Γ 'T? S3p ................... moWsii i

Γη / you T ³ i 3.7488] 0.8828 ΟίΐΓΤ ' 'O4C7 ..........-------- Γ'δο ftSÏÏ 1 3 ~ [0 [ 0-ippm i) ................... 8.8-148 p 80825- 073] [ctü Û.Û372 1 o 't û T Ûpp-p [ ο Γ 0,) 3397 ù'Ï2âë : Ay î 0O®5 i 0.0001 § Ο, ΟΟΰΐ; 0.0010 i (• Ό263 G C24-7] : 20 ppm ) ⁰ ï 0; 0 ρρήι ii Oppin) G ppr 0 ppm : vix 0.0034 i 0.9S99 1 i oasëï] 0 0.0031 i 8.0103 0 / ÏS36] ! i .................... i 0.0321 ) ⁸ ; ³ ; 3aa :: i) 8 ppm) 0 ppm

[Fig-2] shows a variant of [Fig.l] where a part 28 of the partially condensed mixture leaves the exchanger 28 at an intermediate level and is sent to a phase separator 9 ’. The liquid 15 from the separator 9 'is sent after expansion in the valve V3 to the separator 33. The gas from the separator 9' is divided into two, part 30 being returned to the mixture 1 at an intermediate level of the exchanger 25 and the rest 2 being reheated in the exchangers 25, 23 to serve as the first product 2.

The mixture cooled to the cold end of the exchanger 25 feeds column 8 as IL flow

[Fig.3] shows a variant of [Fig.l] where a part 28 of the condensed mixture leaves the exchanger 28 at an intermediate level and is sent to a phase separator 9 ’. The liquid 15 ′ from the separator 9 ′ is sent after expansion in the valve to the separator 33. The gas 30 from the separator 9 ′ is returned to the mixture 1 at an intermediate level of the exchanger 25.

The mixture cooled to the cold end of the exchanger 25 is partially condensed and sent to a phase separator whose gas 11 is used partly as product 2 and partly to supply column 8 as flow 13.

[Fig-4] shows a variant of [Fig 1] where liquid nitrogen 19 is added to the flow 8 after being cooled in the two exchangers 23, 25 until the cold end.

Material balance [fig.l]

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Referred 1 4 7 3 8 2 6 5 Characteristics Units Food n ₂ ln ₂ h ₂ / n 2 (after adding tN ₂ ) h ₂ / n 2 (column exit) First product th ₂ CH-rich gas 4 Gas rich in- N ₂ P bar g 51.9 53.0 5.5 49.7 49.7 49.7 4.0 4.0 T ° C 45 40 185 42 -190 42 42 42 Q Nm ³ / h 203,751 48 100 760 181 353 150 765 56,000 7,393 7,753 Compo mol / mo 1 h ₂ 0.9376 0 0 0.7499 0.9020 0.9734 0, 0407 0, 0807 CO 0.0171 0 0 0.4 PPm 0.0148 0, 0825 0, 2673 ch ₄ 0.0372 0 0 0 ppm 0.0071 0, 8397 0, 1286 Ar 0.0025 0.0001 0.000 1 6 ppm 0.0016 0, 0263 0, 0297 co ₂ 20 ppm 0 0 0 ppm 0 ppm 0 ppm 0 ppm N2 0.0034 0.9999 0.999 9 0.2501 0.0979 0.0031 o, 0108 o, 4936 h ₂ o 0.0021 0 0 0 ppm 0 ppm 0 ppm 0 ppm

Claims (1)

[Claim 1] [Claim 2] [Claim 3] [Claim 4] [Claim 5] [Claim 6] Claims Process for the separation of a hydrogen-rich mixture (1) also containing argon or carbon monoxide or methane or at least one hydrocarbon heavier than methane and optionally nitrogen in which: the mixture is cooled in a heat exchanger (23, 25), at least part of the mixture is condensed to form a two-phase flow, the gas is separated in a phase separator (9, 9 ') to form a gas flow ( 11) rich in hydrogen but depleted in argon or methane or carbon monoxide / or at least one hydrocarbon heavier than methane and at least a first part (2) of the gas flow is heated in the heat exchanger to serve as the first hydrogen-rich product, we send a second part (13), or even the rest, of the gas flow or the rest of the mixture (11) to a washing column (17), we send a flow of liquid nitrogen (21) at the head of the washing column, a hydrogen-rich gas, depleted in argon or methane or carbon monoxide or at least one hydrocarbon heavier than methane and containing nitrogen than l is removed from the head of the washing column 'reheated in the heat exchanger, to serve as a second product (8), possibly a after having mixed it with liquid (19) or gaseous nitrogen, and a liquid flow (10) is taken out of the tank of the washing column. The method of claim 1 wherein the first product (2) contains less than 5% mol of nitrogen, or even less than 1% mol of nitrogen. Process according to Claim 1 or 2, in which the second product (8) contains less methane and / or argon and / or carbon monoxide and / or at least one heavier hydrocarbon than the first product (2) . Method according to one of the preceding claims, in which the first product (2) contains less nitrogen than the second product (8). Method according to one of the preceding claims, in which the hydrogen-rich gas (8) leaves the head of the washing column containing more than 1 mol%. nitrogen, preferably more than 5% mol. nitrogen. Method according to one of the preceding claims, in which the liquid (15, 15 ') is expanded from the phase separator (9, 9'), it is separated in an additional phase separator (33), the gas (37 ) [Claim 7] [Claim 8] [Claim 9] [Claim 10] and the liquid (35) of the additional phase separator in the heat exchanger (23, 25). Method according to one of the preceding claims, in which the frigories are preferably supplied mainly by sending liquid nitrogen (7) from an external source to a phase separator (27) of the method. Industrial process for the separation of a mixture (1) rich in hydrogen, for the synthesis of methanol and for the synthesis of ammonia comprising a process for the separation of a mixture (1) rich in hydrogen according to one of the preceding claims, a process for synthesis of methanol supplied by the first product (2) of the process according to one of the preceding claims and a process for the synthesis of ammonia supplied by the second product (3, 8) of the process according to the same claim. Apparatus for separating a mixture rich in hydrogen also containing argon or carbon monoxide or methane or at least one hydrocarbon heavier than methane and possibly nitrogen comprising a heat exchanger (23, 25) , a phase separator (9, 9 '), a washing column (17), means for sending the mixture to cool and partially condense in the heat exchanger, means for sending at least one part (28) of the partially condensed mixture at the phase separator, means for sending at least a first part of the gas from the phase separator to heat up in the exchanger as the first product (2), means for sending a second part (13), or even the rest of the gas from the phase separator or part of the mixture (11) to the washing column, means for sending a flow of liquid nitrogen at the head of the washing column, means for leaving the head of the column washing a gas (8) rich in hydrogen, depleted laughed in argon or methane or carbon monoxide or at least one hydrocarbon heavier than methane and containing nitrogen and means for sending the hydrogen-rich gas to heat up in the heat exchanger, to serve as a second product ( 3), possibly after having mixed it with liquid nitrogen (19) and means for removing a liquid flow from the tank of the washing column. Unit comprising an apparatus according to claim 9, a methanol synthesis unit, an ammonia synthesis unit, means for sending the first product to the methanol synthesis unit and means for sending the second product to the ammonia synthesis unit.